A typical internal combustion engine, as employed in vehicle propulsion systems, requires a circulation of pressurized fluid or oil through specially configured galleries to provide cooling and lubrication to components such as bearings and piston rings. Lubrication is generally employed to prevent physical contact between neighboring surfaces experiencing motion relative to one another. Oil pressure is also utilized to control various components, such as, for example, a camshaft phaser.
Pressurized engine oil is typically supplied by an oil pump driven mechanically by the engine's crankshaft. When the engine is shut-off, the oil pump ceases to operate, and oil pressure in the galleries rapidly diminishes. Because oil pressure requires time to be reestablished, a subsequent restart of the engine is affected without the necessary oil pressure.
Internal combustion engines are often used as part of propulsion systems in hybrid vehicles with a “start-stop” feature or function. With a “start-stop”, a hybrid vehicle shuts its engine off automatically when the vehicle is either stopped or coasting, in order to conserve fuel, and is then quickly restarted when vehicle acceleration is again required. The frequency of engine starting events in a hybrid vehicle is, thus, greatly increased in comparison with a conventional, non-hybrid vehicle.